<!DOCTYPE html>
<meta name="viewport" content="width=device-width, minimum-scale=1">
<style>
  body {
    width: 1600px;
    height: 1200px;
    margin: 0px;
  }
  #rootScroller {
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: gray;
    position: absolute;
    overflow: auto;
  }
  #content {
    height: 2000px;
    width: 100px;
    background-color: red;
  }
  #target {
      position: absolute;
      left: 0;
      top: 100vw;
      width: 100vw;
      height: 100px;
      background-color: blue;
  }
</style>
<div id="rootScroller">
  <div id="content"></div>
  <div id="target"></div>
</div>
